1. Field
The present disclosure generally relates to an optical reflector to facilitate an optical source. More specifically, the present disclosure relates to an optical reflector based on a directionally coupled optical loop with evanescent coupling between arms of the optical loop.
2. Related Art
Optical interconnects or links based on silicon photonics have the potential to alleviate inter-chip communication bottlenecks in high-performance computing systems that include multiple processor chips and memory chips. This is because, relative to electrical interconnects, optical interconnects offer significantly improved: bandwidth, density, power consumption, latency, and range.
In order to make a very low-power (for example, less than 1 pJ/bit) optical interconnect, a high-efficiency optical source, such as a semiconductor laser or a laser source, is typically required. In particular, the required power consumption of the laser source may need to be 0.4 pJ/bit.
One approach to fabricating a high-efficiency optical source is to integrate a III-V material with silicon optical-waveguide devices to form a laser cavity. In such a hybrid optical source, the III-V material provides optical gain, and the silicon optical-waveguide devices control the lasing wavelength and the cavity reflection/transmission. In order to minimize the lasing threshold and/or to maximize the lasing efficiency, the cavity reflection/transmission typically needs to be optimized based on the III-V material gain and the cavity loss. Usually, the cavity reflection/transmission is controlled by a partial optical reflector. However, while existing silicon ring-resonator filters provide excellent narrow-band optical filtering for lasing wavelength control, to date implementing a suitable partial optical reflector typically requires two discrete components (a reflector with high reflectivity and a 2×2 directional coupler) to control cavity reflection and establish output port(s) for the hybrid laser. Moreover, using a separate 2×2 directional coupler usually results in longer cavity length and the laser output is split into two output ports with different power.
Hence, what is needed is an optical reflector without the problems described above.